Léopold Victor Delisle (24 October 1826, Valognes (Manche) – 21 July 1910, Chantilly, Oise), was a French bibliophile and historian.
He was taken on as a young man by the antiquarian and historian of architecture, Charles-Alexis-Adrien Duhérissier de Gerville, who engaged him to copy manuscripts in his collection, and taught him enough of the basics of paleography that he was able to gain entrance to the École des Chartes in 1846. At the École des Chartes, where his career was remarkably brilliant, his valedictory thesis was an Essai sur les revenus publics en Normandie au XIIe siècle (1849), drawn in part from manuscripts of Duhérissier de Gerville, and it was to the history of his native Normandy that he devoted his early works. Of these the Études sur la condition de la classe agricole et l'état de l'agriculture en Normandie au Moyen Âge (1851), condensing an enormous mass of facts drawn from the local archives, was reprinted in 1905 without change, and remains authoritative.
In November 1852 he entered the manuscript department of the Bibliothèque imperiale (nationale), of which in 1874 he became the official head in succession to Jules Taschereau. He was already known as the compiler of several invaluable inventories of its manuscripts. When the French government decided on printing a general catalogue of the printed books in the Bibliothèque, Delisle became responsible for this undertaking and took an active part in the work; in the preface to the first volume (1897) he gave a detailed history of the library and its management.
Under his administration the library was enriched with numerous gifts, legacies and acquisitions, notably by the purchase of a part of the Ashburnham manuscripts. Delisle proved that the bulk of the manuscripts of French origin which the Earl of Ashburnham had bought in France, particularly those bought from the book-seller Jean-Baptiste Barrois, had been purloined by Count Libri, inspector-general of libraries under King Louis-Philippe, and he procured the repurchase of the manuscripts for the library, afterwards preparing a catalogue of them entitled Catalogue des manuscrits des fonds Libri et Barrois (1888), the preface of which gives the history of the whole transaction. He was elected member of the Academie des Inscriptions et Belles Lettres in 1859, and became a member of the staff of the Recueil des historiens de la France, collaborating in vols xxii. (1865) and xxiii. (1876) and editing vol. xxiv. (1904), which is valuable for the social history of France in the 13th century.